Deposition of copper wiring in integrated circuits involves a number of processes. Typically, a trench or hole is etched into dielectric material located on a substrate wafer. Then, the hole or trench typically is lined with one or several adhesion and diffusion-barrier layers; for example, with tantalum nitride, TaN. The hole or trench then is lined with a thin layer of copper, Cu, that acts as a seed layer for electroplated copper. Thereafter, the hole or trench is filled with copper, typically by an electroplating process.
While copper is useful as a seed layer for the plating of copper, it has the disadvantage that a diffusion barrier layer is required to prevent diffusion of copper into other parts of the integrated circuit. One of the major challenges in the field of copper-based interconnects in semiconductor manufacturing is the identification and deposition of a material that could not only serve as a diffusion barrier to copper migration into adjoining dielectric layers, but would also serve as a seed layer for direct copper plating. Preferably, a material suitable for use as both a diffusion barrier and a seed layer would adhere well to dielectric materials used in integrated circuits.
A thin film of ruthenium metal deposited on a wafer substrate is useful as a diffusion barrier layer to inhibit or to prevent diffusion of copper into adjoining dielectric layers. In the past, the formation of ruthenium on dielectric material has been problematic. The deposition of a metal thin film, particularly of ruthenium, Ru, or other Ru-containing layer, by chemical vapor deposition (such as CVD and ALD) directly onto a dielectric material often resulted in poor morphology of the thin film. The plating of copper directly onto a ruthenium seed layer has also been problematic in the past. Copper that is plated directly onto a conventional ruthenium-containing layer often shows poor adhesion to the ruthenium-containing layer. Also, the relatively high resistivity of a conventional ruthenium-containing layer, compared to a conventional copper seed layer, typically increases the undesired terminal effect during copper plating. As a result, electroplated copper deposits unevenly on the wafer substrate and electrofilling of high aspect ratio features is unsatisfactory. Undesired void spaces in metal-filled features are common.
In the past, adhesion layers, barrier layers and copper seed layers lining holes and trenches were deposited using conventional physical vapor deposition techniques. As the design density of integrated circuits increases, resulting in smaller dimensions of holes and trenches, it is generally more difficult to use physical vapor deposition to line holes and trenches with uniform and conformal thin films of integrated circuit material. As a result, deposition of metal, particularly ruthenium metal and other ruthenium-containing compounds, by chemical vapor deposition (CVD) and atomic layer deposition (ALD) is important for achieving good circuit quality and acceptable manufacturing yields.
Chemical vapor deposition of metal directly onto a dielectric material, such as silicon oxide, SiO2, or onto standard adhesion layer material, such as tantalum nitride, TaN, is often accompanied by delayed and discontinuous growth, surface roughness and poor adhesion. These problems are especially acute in processes for depositing ruthenium on silicon oxide (SiO2). Many other metal CVD processes, for example, MOCVD of copper, suffer these problems also.
Co-owned and co-pending U.S. patent application Ser. No. 10/821,751, which is hereby incorporated by reference, teaches a plasma treatment of an integrated circuit substrate that improves ruthenium metal deposition by CVD or ALD, particularly onto dielectric material. The plasma treatment reduces the time required for nucleation of ruthenium metal on the substrate surface during a chemical vapor deposition process, thereby decreasing the nucleation delay of metal growth on the substrate surface. Improved nucleation of metal improves surface morphology of deposited metal, allowing thinner films to be continuous. Further, plasma treatment generally decreases the deposition rate of metal onto the plasma-treated surface, thereby improving control of the growth and thickness of metal films, especially ultra-thin films such as seed layers. It is believed that plasma treatment of a surface with excited species (e.g., excited iodine species) suppresses the subsequent deposition rate of ruthenium or other metal on the treated surface, resulting in less “island” growth and more uniform layer growth. Plasma treatment of a substrate surface improves adhesion of deposited metal to the substrate surface. Improved morphology and greater smoothness of deposited metal improves adhesion of materials subsequently formed in contact with the metal. As a result, overall film-stack adhesion is enhanced.
There exists a need for making a conductive layer that can serve as an adhesion layer and a barrier layer and also as a seed layer for electroplating of copper or other plating metal.